November 19, 2015 How would you define “work” in your own words? How would you define “power” in your own words? AFTER you have finished both bell ringers, please pick up the new packets on the front table.

Today Eureka Episode Notes: Introduction to Work & Power Homework: Part 3&4 of HW Packet Important Dates: Work & Power Quiz 11/23

GOALS To define work and power To calculate work and power To determine if work is done in given situations

WORK Work is done when a force causes a change in motion of an object. Work is a force that is applied to an object multiplied by the distance of movement of the object. In order for work to be done, the force must be applied in the direction of the motion of the object. When doing problems, make sure you are using the force that is in the direction of motion. Drawing a picture would be helpful.

W = F x d WORK WORK FORCE DISTANCE = x (Meters) (Newtons) W = F x d *** This is NET FORCE, so you might need to draw a picture to determine the net force! W F d

WORK If we apply a force on an object that does not move, no work has been done. Sitting and looking at a computer screen is not work. Tapping on the keyboard and making the keys move is work. Your fingers are moving and applying a force in the direction of motion. (down)

PRACTICE PROBLEM If a father lifts his child 2.0m into the air and exerts a force of 190N, what is the work done by good old dad? Given? F = 190 N d = 2.0 m W = ? Equation? W = F x d Solve. W = (190 N)(2.0 m) W = 380

WORK Units: As you can see, the units will be N-m. A N-m is also known as a Joule (J) Both work and energy are expressed in units of joules (J).

POWER Power is a measure of the rate at which work is done HOW FAST work is being done Power is the amount of work done in a certain amount of time The same amount of work done faster (less time) will produce more power Inversely related

POWER POWER WORK TIME = / (Joules) (Seconds) P = W t W P t

PRACTICE PROBLEM It takes 100 J of work to lift an elevator 18 m. If this is done in 20 s, what is the average power of the elevator? Given? t = 20 s W = 100 J P = ? Equation? P = W/t Solve. P = 100 J/20 s P = 5

POWER Units: As you can see, the units would be J/s. 1 J/s is known as a Watt (W) One watt is the amount of power required to do 1 joule of work in 1 second, or watt = 1 joule/1 second

HOMEWORK Homework packet part 3&4